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Klier, Lydia; Ziegler, Dorothee S.; Rahimofft, Rene; Mosrin, Marc; Knochel, Paul (2017): Practical Large-Scale Regioselective Zincation of Chromone Using TMPZnCl center dot LiCl Triggered by the Presence or Absence of MgCl2. In: Organic Process Research & Development, Vol. 21, No. 4: pp. 660-663
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Chromones are efficiently zancated in position C(3) in THF by using the commercially available amide base TMPZnCl center dot LiCl (TMP = 2,2,6,6-tetramethylpiperidyl). Additionally, in the presence of a Lewis acid such as MgCl2, zincation using TMPZnCl center dot LiCl occurs at C(2). These metalation reactions are carried out on a SO mmol scale, and the metalation selectivities have been compared with the corresponding small-scale reactions (2 mmol). The resulting zinc organometallics undergo smooth reactions with various electrophiles, for example, Pd-catalyzed cross-coupling reactions or Cu-catalyzed acylations or allylations.